test/gc/g1/TestEagerReclaimHumongousRegions.java

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/*
 * @test TestEagerReclaimHumongousRegions
 * @bug 8027959
 * @summary Test to make sure that eager reclaim of humongous objects work. We simply try to fill
 * up the heap with humongous objects that should be eagerly reclaimable to avoid Full GC.
 * @key gc
 * @library /testlibrary
 */

import java.util.regex.Pattern;
import java.util.regex.Matcher;
import java.util.LinkedList;

import com.oracle.java.testlibrary.OutputAnalyzer;
import com.oracle.java.testlibrary.ProcessTools;
import com.oracle.java.testlibrary.Asserts;

class ReclaimRegionFast {
    public static final int M = 1024*1024;

    public static LinkedList<Object> garbageList = new LinkedList<Object>();

    public static void genGarbage() {
        for (int i = 0; i < 32*1024; i++) {
            garbageList.add(new int[100]);
        }
        garbageList.clear();
    }

    // A large object referenced by a static.
    static int[] filler = new int[10 * M];

    public static void main(String[] args) {

        int[] large = new int[M];

        Object ref_from_stack = large;

        for (int i = 0; i < 100; i++) {
            // A large object that will be reclaimed eagerly.
            large = new int[6*M];
            genGarbage();
            // Make sure that the compiler cannot completely remove
            // the allocation of the large object until here.
            System.out.println(large);
        }

        // Keep the reference to the first object alive.
        System.out.println(ref_from_stack);
    }
}

public class TestEagerReclaimHumongousRegions {
    public static void main(String[] args) throws Exception {
        ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(
            "-XX:+UseG1GC",
            "-Xms128M",
            "-Xmx128M",
            "-Xmn16M",
            "-XX:+PrintGC",
            ReclaimRegionFast.class.getName());

        Pattern p = Pattern.compile("Full GC");

        OutputAnalyzer output = new OutputAnalyzer(pb.start());

        int found = 0;
        Matcher m = p.matcher(output.getStdout());
        while (m.find()) { found++; }
        System.out.println("Issued " + found + " Full GCs");
        Asserts.assertLT(found, 10, "Found that " + found + " Full GCs were issued. This is larger than the bound. Eager reclaim seems to not work at all");

        output.shouldHaveExitValue(0);
    }
}